The presented invention generally pertains to a wafer carrier designed for supporting, constraining, storing, and precisely positioning semiconductor wafer disks for use in the production of integrated circuits and a method for assembling the same. More specifically, the invention pertains to a low tolerance build-up wafer carrier that utilizes press-fit fasteners for connecting carrier components.
The transformation of wafer disks into integrated circuit chips often involves several steps where the disks are repeatedly processed, stored and transported. Due to the delicate nature of the disks and their extreme value, it is vital that they are properly protected throughout this procedure from contaminants. One purpose of a wafer carrier is to provide protection from these contaminants.
Since the processing of wafer disks is generally automated, it is essential for the carrier to precisely align the wafer disks according to the specifications of the processing equipment being used. The tolerances available to the carrier are generally very tight, around 0.20 inch, for proper interaction between the processing equipment and the wafer disks. The wafer carrier manufacturing industry constantly strives to design carriers with improved tolerances for better assurance of accurate carrier-equipment alignment.
Tolerance build-up or stacking often results when an aggregate of several parts is assembled. The resulting gap, grip, or interference is related to the dimensions and tolerances of the individual parts. The greater the tolerances of the individual parts the greater the likelihood that a gap or interference will result. Consequently, one must minimize the number of components used in order to minimize the tolerance build-up or stacking of these gaps and interferences.
Carriers may be of a single mold design or of a composite design made of several small individually molded parts. The problem of tolerance build-up clearly lies with the composite carrier due to the multiplicity of parts. In addition, composite carriers generally require fasteners to join the components introducing even more parts and further increasing tolerance build-up. Consequently, there is a need for a fastener for assembling composite wafer carriers that does not lead to tolerance build-up.
It is common to use screws to assemble composite wafer carriers. Problems exist with the use of these fasteners. First, over tightening the screws can lead to distortion of the carrier causing an increase in tolerance build-up. Second, it is time consuming to fasten components with screws. Consequently, there exists a need for a fastener that does not lead to distortion and can quickly fasten carrier components together.
Even though composite carriers are more susceptible to tolerance build-up than single mold carriers, single mold carriers still have their problems. Single mold carriers are more prone to warping than composite carriers due to the larger molds. Due to the difficulty in controlling the warping of single mold carriers and in predicting the extent to which the warping will affect the resulting product, it is often desirable to use the more predictable composite carrier design. By dividing up a single mold carrier into smaller, separately molded components, warping can be reduced and tight specifications can be met with greater consistency.
Generally, wafer carriers include an equipment interface portion, such as a guide plate or kinematic coupling, for properly orienting the carrier with respect to carrier interface portions provided by the processing equipment. Guide plates are often integrated into single mold carriers. Separating these equipment interfaces from the rest of the carrier design reduces the size of the molded parts, thus reducing the potential for warping. Consequently, there exists a need to have separate equipment interface portions that can be attached to single mold wafer carriers without tolerance build-up making it easier to meet critical carrier specifications.
Besides having a tendency to increase warping in single-mold carrier designs, equipment interfaces such as kinematic couplings are also susceptible to flexing when carrying the weight of the carrier. This flexing causes undesired shifting in the position of the carrier causing a tolerance build-up and increasing the potential for carrier-equipment mismatch. Consequently, there is a need for a carrier, capable of interfacing with processing equipment, that is not susceptible to the flexing of an attached kinematic coupling.
The present invention provides a wafer carrier and method for assembling the same for fulfilling the needs outlined above.
It is an object of the invention to reduce tolerance build-up by connecting carrier-related components with press-fit fasteners.
Another object of the invention is to provide interface contact portions on the carrier which directly contact the carrier interface portions for more accurate carrier-equipment alignment.
Still another object of the invention is to provide a carrier designed to avoid alignment problems associated with guide plates flexing under the weight of the carrier.
Another object of the invention is to attach a guide plate to the carrier with press-fit fasteners to reduce tolerance build-up.
Yet another object of the invention is to provide a composite wafer carrier having lower assembly costs.
Another object of the invention is to provide a method for assembling a composite wafer carrier with press-fit fasteners.
Still another object of the invention is to provide a fastener that can quickly attach carrier components together.
A wafer carrier interfaces with processing equipment or the like by way of an equipment interface portion which confronts a corresponding cooperating machine interface portion on processing equipment. In a preferred embodiment, cooperating machine interface portions are guided to pairs of interface contact portions positioned on the interface side of the carrier.
In another preferred embodiment, fasteners comprising a first portion integral with a first element and a second portion integral with a second element are used to attach the first and second elements together without tolerance build-up. These fasteners are used for assembling composite wafer carriers and for attaching equipment interfaces to carriers.